Ink-jet recording is carried out by impinging micro-droplets employing various working principles and attaching them onto a recording sheet of paper to record images, letters and the like, and exhibits advantages such as relatively high speed, low noise, easy practice for multicolor, and the like. Regarding this method, conventional problems with clogging of a nozzle and maintenance have been overcome by improvements in both aspects of the ink and instrument, and at present, it has been increasingly employed in various fields such as printers, facsimile machines and computer terminals and the like.
The ink-jet recording sheet employed for the ink-jet recording method has been generally needed to meet requirements such that the density of a printed dot is high and the hue is bright and clear; ink is quickly absorbed and when printed dots are superimposed, ink neither flows nor spreads; diffusion of the printed dot in a horizontal direction is not larger than that required and the border is smooth and causes no unclearness and the like.
As the ink-jet recording sheet, various kinds of ink-jet recording sheets have been employed. For example, there have been employed ordinary paper, various coated paper (art paper, coat paper, cast-coat paper, etc.) prepared by coating a layer comprising a hydrophilic binder and an inorganic pigment on a paper support. Furthermore, there has been employed recording sheets prepared by coating an ink absorptive layer as a recording layer on various supports such as the above-mentioned paper, various kinds of transparent or opaque plastic film supports or various supports prepared by covering both sides of paper with a plastic resin.
The above-mentioned ink absorptive layer is divided into two main groups, that is, one is a so-called swelling-type ink absorptive layer mainly composed of a hydrophilic binder and the other is a void-type ink absorptive layer having a void-containing layer in the recording layer.
The advantages of the swelling type ink absorptive layer is that after an ink solvent (water and high boiling point solvent) is perfectly vaporized, remarkably high glossiness and high density are obtained. On the other hand, the ink-absorbing rate is smaller than that of the void type recording sheet mentioned below,, and there is a problem in which in a high ink density region, image quality is liable to be deteriorated due to the formation of roughness caused by beading and the like. Furthermore, the vaporization of an ink solvent, especially high boiling point organic solvent, is extremely slow and after printing, the high boiling point organic solvent remains in a hydrophilic binder for some time. Thus, there is a problem with the fact that the hydrophilic binder is left under a swelled and wet state for a long period of time.
As a matter of fact, for several hours after printing, in some cases, for several days after printing, the situation is that it is impossible to rub strongly the printed surface or to stack a sheet of paper on it.
On the other hand, the void type ink absorptive layer has voids in the recording layer to result in great ink absorbability. Accordingly, as compared to the swelling type, the image beading hardly occurs in the high ink density area and the degradation of the image quality in the high density area is small.
Furthermore, when the void type ink absorptive layer has a sufficient void volume as compared to that of the ink, the surface immediately after printing works, as if it is dried, even though an organic solvent remains in the void structure. Thus, it would be possible to touch the surface and to bring printed sheets into contact each other.
Because as this type of ink absorptive layer, a relatively high transparent layer is formed, fine particles having a low refractive index (refractive index of 1.6 or less is particularly preferred.) and further a small diameter (200 nm or less is particularly preferred.) are preferably employed. Of particles, fine particle silica which meets such conditions is particularly preferably employed, since it forms efficiently voids, and further, enables to obtain relatively high glossiness and an image having high maximum density.
As conventional techniques in which the above-mentioned inorganic fine particles having a small diameter are employed in the ink-jet recording sheet, colloidal silica is described, for example, in Japanese Patent Publication Open to Public Inspection Nos. 57-14091, 60-219083, 60-219084, 61-20797, 61-188183, 63-178084, 2-274857, 4-93284, 5-51470, 5-278324, 6-92011, 6-183131, 6-183134, 6-297830, 7-17125, 7-52526, 7-81214, 7-101142, 7-117335, 7-179029, 7-137431, 8-25800, 8-67064, 8-118790; fine silica particles prepared by a gas phase method are described in Japanese Patent Publication No. 3-56552, Japanese Patent Publication Open to Public Inspection Nos. 63-170074, 2-13986, 2-187383, 2-188287, 7-276789, 8-34160, 8-132728, 8-174992, porous alumina or its hydrate described in, for example, Japanese Patent Publication Nos. 3-24906, 3-24907, 6-98844, 7-2430, 7-121609, Japanese Patent Publication Open to Public Inspection Nos. 60-2455882-43083, 2-198889, 2-263683, 2-276671, 3-215081, 3-215082, 3-281383, 3-281384, 3-284978, 4-67985, 4-67986, 4-92813, 4-115984, 4-202011, 4-267179, 4-263981, 4-263982, 4-263983, 4-267180, 4-308786, 4-320877, 4-3230754-345883, 5-16517, 5-24335, 5-24336, 5-32037, 5-32413, 5-32414, 5-50739, 5-124330, 5-301441, 6-55829, 6-183133, 6-183135, 6-183126, 6-199034, 6-199035, 6-255235, 6-262844, 6-270530, 6-297831, 6-183187, 6-48016, 7-76162, 7-89216, 7-89211, 7-76161, 7-108754, 7-125412, 7-164730, 7-172038, 7-232473, 7-232474, 7-232475, 7-237248, 7-246769, 7-276783, 7-290816, 7-304249, 8-2087, 8-2090, 8-2091, 8-2093, 8-25796, 8-72388, 8-90900, 8-108614, 8-112964,8-197832, 8-258397, etc.; fine particulate calcium carbonate described in, for example, Japanese Patent Publication Open to Public Inspection Nos. 57-120486, 57-129778, 58-55283, 61-20792, 63-57277, 4-250091, 3-251487, 4-250091, 4-260092, 7-40648, etc. and the like.
Of these, when the fine particle silica is employed, the decrease in density of recorded images is smallest and clear color images having a high maximum density is obtained.
The ink-jet recording sheet comprising a support having thereon the above-mentioned void type ink absorptive layer is excellent in resulting in particularly high glossiness, high void ratio and high maximum density. In addition to those, when a support having relatively good flatness is employed, the ink-jet recording sheet having a high glossy surface is obtained. On the other hand, the water-soluble dye is employed. Therefore, there is caused a problem in that when stored at high temperature and humidity for a long period of time after printing or attached with a water droplet, the dye blots.
In order to improve the water resistance and moisture resistance of the dye, heretofore, there have been proposed various methods to fix the dye. A particularly effective method is that an aqueous solution containing uniformly a polymer having a tertiary or quaternary nitrogen atom or its particulate latex is added.
For example, Japanese Patent Publication Open to Public Inspection No. 57-36692 describes an ink-jet recording sheet which is prepared by coating a coating solution comprising a basic mordant and gelatin as one part of a binder as an ink-receiving layer on a support such as paper base or polyethylene terephthalate film.
Japanese Patent Publication Open to Public Inspection No. 53-49113 describes an ink-jet recording sheet for aqueous ink in which polyethyleneimine is impregnated into paper inside.
Japanese Patent Publication Open to Public Inspection No. 58-24492 describes a recording material comprising an electrolyte polymer having a cation or anion group.
Japanese Patent Publication Open to Public Inspection No. 63-224988 describes a recording material in which an ink-receiving layer comprises a primary or tertiary amine, or a quaternary ammonium salt, and the pH of an ink-holding layer ranges from 2 to 8.
Japanese Patent Publication Open to Public Inspection No. 63-307979 describes an ink-jet recording sheet comprising a layer comprising a hydrophilic polymer mordant having a tertiary or quaternary nitrogen atom and a polymer having a hydrophilic group.
Japanese Patent Publication Open to Public Inspection Nos. 59-198186 and 59-198188 describe recording materials in which a polyethyleneimine organic salt is incorporated in a base material or a coating layer on the base material.
Japanese Patent Publication Open to Public Inspection No. 60-46288 describes an ink-jet recording method employing a recording material comprising an ink containing a specified dye, polyamine, etc.
Japanese Patent Publication Open to Public Inspection Nos. 61-61887, 61-72581, 61-252189 and 62-174184 describe ink-jet recording sheets comprising polyacrylamine.
Japanese Patent Publication Open to Public Inspection No. 61-172786 describes an ink-jet recording material comprising a polymer having an intermolecular hydrogen bond (gelatin, polyethyleneimine, etc.) and a polymer having no intermolecular hydrogen bond (polyethylene glycol, polyvinylpyrrolidone, etc.).
Japanese Patent Publication Open to Public Inspection No. 63-162275 describes an ink-jet recording sheet in which a cationic polymer and a cation surface active agent are coated on a support or impregnated into the support.
Japanese Patent Publication Open to Public Inspection No. 6-143798 describes an ink-jet recording sheet in which a dye-fixing layer mainly composed of a quaternary ammonium salt polymer and a cation-modified polyvinyl alcohol is provided on a plastic support and a dye-penetrating/ink absorptive layer is provided thereon.
Furthermore, Japanese Patent Publication Open to Public Inspection Nos. 59-20696, 59-33176, 59-33177, 59-96987, 59-155088, 60-11389, 60-49990, 60-83882, 60-109894, 61-277484, 61-293886, 62-19483, 62-198493, 63-49478, 63-115780, 63-203896, 63-274583, 63-280681, 63-260477, 1-9776, 1-24784, 1-40371, 3-133686, 6-234268, 7-125411, etc. describe that each of specified polymers or compounds comprising a tertiary or quaternary nitrogen atom is added to an ink-receiving layer.
Such techniques to fix a dye described in the prior art exhibit an effect worthwhile fixing the dye. However, there have been a problem caused by employing the cationic polymer.
Namely, when in order to accomplish the high ink absorbability, a large amount of inorganic fine particles is employed on a support, aggregation between the fine particles and the cationic polymer is caused to be liable to form coarse particles. Accordingly, even though a recording layer is formed by coating such coating solution on a support, a problem is caused in that good glossiness is hardly obtained.
Japanese Patent Publication No. 2-188287 describes that an ink-jet recording sheet which exhibits consistent image quality and high recording density, while keeping appearance and touch like paper is prepared by providing on an ink-absorbing support, a layer prepared by mixing dehydrated silica comprised of ultra-fine particles with a cationic polymer.
However, when the technique described in the above-mentioned patent is only employed, aggregate is liable to be formed and high glossiness on a recording layer is hardly obtained. When obtaining the appearance as described in the above-mentioned patent is only set as an object, such technology alone would meet fully the requirements. However, it is not sufficient to obtain high glossiness as exhibited in photographic prints and the like.